The discussion throughout this specification comes about due to the realisation of the inventors and/or the identification of certain prior art problems by the inventors.
The applicants are aware of a number of transponder systems that provide two dimensional, limited three dimensional or full three dimensional capability. These systems utilise a multiplicity of interrogator coils operating in different coordinate axis, to achieve two or three dimensional operation.
One particular interrogator design produces a uniform field in three dimensions. This form of interrogator is known as a Tunnel Reader Programmer (TRP). An example of a TRP for interrogating transponders on pallets or conveyors which meets all OH&S and EM regulations in Australia is disclosed in U.S. Pat. No. 5,258,766 and international application PCT/AU95/00436.
While a TRP has three dimensional interrogation properties, it is suitable for applications where the RFID transponders are moved in and out of the TRP, usually on a conveyor or similar. TRP are inherently unsuitable for applications requiring the interrogator to operate on a flat surface such as a table or wall. For these applications flat planar antenna coils are required however these coils suffer from producing fields in only one direction at any point relative to the coil and do not have a three dimensional interrogation capability.
FIG. 1 illustrates a conventional planar antenna coil arrangement, in which the coil 10 has windings 11 arranged in a somewhat circular configuration.
FIG. 2 illustrates a cross sectional view X of FIG. 1 of the windings of the coil of FIG. 1. The magnetic field created by inducing power into the windings is represented 12. If a transponder 13 has a coil (not shown), but placed on it's outer top surface, for example, and if the transponder 13 is positioned substantially horizontally between the windings as illustrated in FIG. 2, the field 12 produced by the windings 11 has a correct orientation to power to transponder. Equally, if a transponder 14 is placed in a substantially vertical orientation as illustrated in FIG. 2, it too will be powered by the field 12. However, if a transponder 15 is placed substantially horizontally near or outside the windings 11, the field 12 generated by the windings will not be correctly oriented to power the transponder 15. Likewise if the transponder is placed in a substantially vertical orientation in the inside of the windings 11 and 12 as illustrated in 16, the field 12 generated by the windings will not be correctly oriented to power the transponder 15.
If RFID and remote powering is used in applications where orientation of the items to be identified cannot be guaranteed, such as shelving and storage systems, document tracking, luggage identification, gaming tokens, by way of example only, the above identified problem can lead to items being missed, that is, not correctly identified.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.
An object of the present invention is to provide an antenna design and/or interrogator which is more likely to enable powering and/or communication with an RFID device.
A further object of the present invention is to alleviate at least one disadvantage associated with the prior art.